Tightening cylinder head bolts by angle rather than torque.

Can anybody explain the logic of the angle plate method of doing cylinder head bolts instead of torque wrench? Surely tightening by a given angle must translate to a specific torque figure?

My question is a bit academic now as I've just used the angle plate method and although it was much easier than I expected I would have preferred a single torque figure to work with.

Any information welcome.

Cic.

Reply to
Cicero
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Angle tightening overcomes the problems of high torque (in relation to the bolt size) and friction between the item and the bolt head. This friction can easily give a very false reading on a torque gauge, which is why you should carefully follow the design parameters of the bolt system when using a torque wrench, such as specific lubrication on threads and below bolt head/special washer, and only ever torque from one stage to another as specified.

Angle tightening precludes so much care being needed and still gets a good seal.

Generally Angle tightening is used on specifically designed new bolts, such as cylinder head bolts. The angle puts a certain amount of stretch or spring into the bolt, this holds the head down and keeps it down, even through expansion/contraction. Angle tightened bolts will generally (always? ) not need any additional tightening after use , whereas old torque tightened bolts did need a check after a period of use.

The method of tightening is as specified by the bolt/manufacturer, you can't just use any old figure and expect the desired outcome.

If the bolt is new or within parameters and is specified for angle tightening then use the angle method If the bolt is not in parameters or is specified for single use then replace it, or if you are a pikey then just re-use it, torque it down to 75 lbft and hope for the best (very common practise in a lot of places since a new set of bolts will buy a good few drinks)

Mrcheerful

Reply to
mrcheerful

Do a google for 'Torque to Yield".

But basically it's a method of optaining a far more predictable tension on a fastener, as a conventional torque setting is influenced too much by external factors.

Reply to
moray

If you know you want to stretch the bolt by a certain amount that translates directly into a certain number of degrees rotation.

Reply to
adder1969

The message from Cicero contains these words:

Yes, it does - and then again it doesn't. What is wanted is a particular compression of the gasket and, more importantly, a particular load on the bolts.

Using a torque wrench particularly at high torques is very dependent on the condition of the bolt, greasiness, rustiness, dirt in the threads etc.

Angle however takes a reasonably reliable starting point and then adds a distance (1/4 of the pitch of the thread, usually) to it - which is a much more accurate way of loading a bolt.

Reply to
Guy King

Thanks for all replies and the information supplied. The picture is much clearer now. I hope that the 5 stage process detailed in the manual works as intended, especially as the cost of parts is really quite high for such a simple repair. Head gasket was about 22 GBP and set of head bolts nearly

17 GBP. One benefit is that there's no need to re-torque the head bolts, unless the manual has omitted to say so, which seems unlikely with such a detailed description of the process.

Reply to
Cicero

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